I have a nice desk top that is probably pine? that I want to turn into a desk. I bought two A shaped frames at IKEA to attach to the table top. I have no idea how to attach the table top to the frames without the screw or whatever I use to attach it showing through the desk top? Do i use a really long, heavy screw that can go through the A frame at an angle, but doesn't go all the way through the desk top? Please help; I am new to woodworking, etc.

Nevermind my first comment, I did not read the question correctly :) Are there any screw holes through the A-frame leg top bar? If not, how do the tops provided by the supplier mount to the frame?
– Ashlar♦Oct 6 '16 at 21:07

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Just put the board on top of the support frames. Gravity will keep it in place.
– Ast PaceOct 7 '16 at 2:29

2 Answers
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You actually don't even need to attach them. A frames are designed to not tip over so two of them will just let your desk top lay on it without any problem.

However If you're going do some rough stuff on it i suggest you just buy some smaller screws. Measure to know the size. About half in your table top. Measure the screws in the store before you buy them.
Get a drill bit for pilot holes about as thick as the screws' middle. If you don't drill a hole first there is a good chance your A frames or tabletop will crack. Then use tape to match the depth of the pilot holes with the screws so you stop before you drill through the desktop. Then simply screw the screws in.

You can also do it with dowels, divide the dowels in two, take a drill bit a tiny tiny bit smaller then your dowels use tape to determine depth. Drill the holes. Then put wood glue on it and assemble it.

Again, i don't think you need to do all of that but that are some options.

A simple solution to prevent sliding would be to screw some rubber things into the A frames, 2 for each frame will work.

There are various ways this can be done, including screwing right through the frames into the tabletop as you asked about 9with a few tweaks). Probably the easiest solution for you will be to use what are called expansion plates, see image on the right in this previous Answer.

These will be screwed into the A-frames (two screws per) and then into the tabletop (one screw in each). You would often do the last step with the tabletop face-down on the floor (protect it from denting by laying it onto a blanket or similar) so that you don't have to crawl under and try to drive the screws in from underneath, which can be tricky to do properly and is anyway uncomfortable unless you're a contortionist.

You'll need four of these plates. They usually come with their own screws but if not you'll need to buy some. Don't be tempted to use drywall screws, they're a little too brittle to rely on for woodworking applications.

Remember the screws that will go upwards into the tabletop must be short enough not to poke through the top when driven home! You'd be amazed the number of times people have not taken this into account, even experienced woodworkers sometimes forget.

Note: if your top is made from solid wood and not a manmade board material with a veneer you'll need to use the slots that run perpendicular to the grain, not the ones that run parallel to the grain (that would defeat the purpose of using these plates). If your board is plywood or another board material it doesn't matter which slots you use as the top won't expand and contract with changes in humidity the way that solid wood does.